Knight Lore: Routine at B73C

B73C: Handle Guard Moving East West

Handles the top half of a guard that patrols east and west. The guard walks at a speed of 02 and turns round when it hits something. The bottom half of the guard, which is the next object in the table, is kept in step.

Input
IX	Address of the top half of the guard

Walk east or west and turn when the guard hits something.

HandleGuardMovingEastWest

B73C

CALL SetPixelAdjustments_Guard

Set the pixel adjustments of a guard.

B73F

BIT 0,(IX+$0D)

Test whether the guard is heading east.

B743

LD A,$02

Set the speed to 02.

B745

JR NZ,HandleGuardMovingEastWest_Speed

Jump to HandleGuardMovingEastWest_Speed if the guard is heading east.

B747

NEG

Make the speed negative.

HandleGuardMovingEastWest_Speed

B749

LD (IX+$09),A

Set the speed in X of the guard.

B74C

LD (IX+$29),A

Set the speed in X of the bottom half of the guard too.

B74F

CALL FaceDirectionOfMovement

Choose the graphic of the guard from its direction.

B752

CALL ApplyGravityAndMove

Apply gravity to the guard and move it.

B755

BIT 0,(IX+$0C)

Jump to HandleGuardMovingEastWest_BottomHalf if the guard has not hit something along the X axis.

B759

JR Z,HandleGuardMovingEastWest_BottomHalf

B75B

LD A,(IX+$0D)

Fetch the direction flags of the guard.

B75E

XOR %00000001

Turn the guard round.

B760

LD (IX+$0D),A

Store them.

Keep the bottom half in step and make the guard deadly.

HandleGuardMovingEastWest_BottomHalf

B763

LD A,(IX+$01)

Fetch the X coordinate of the guard.

B766

LD (IX+$21),A

Give it to the bottom half of the guard.

B769

JP SetDeadlyFlagsAndDraw

Make the guard deadly and flag it to be drawn again.